When we checked in last week, the CM at the Outpost asked me if we like the 800 loop. I said yes, is that what we got assigned? She said she was just looking back at our previous stays and saw we were there before. She asked if we liked the last site we stayed in and would have given us that one, except that the folks in front of us had just been assigned that. So she put us right next to them.
I know we have discussed many times that they assign the sites before we arrive. But this and a couple of other experiences I have had seem to indicate otherwise, and would mean it never hurts to request your favorite when you are sitting there checking in.
Rog is right (of course) about asking to be moved if you find something that will work better for you. You don't have to go back up to the desk to do so. Just use a house phone at the comfort station. Tell them site assigned and the site you would like to have and see what happens. Only once have they told me no, and that was because the site was already occupied, although they had no stuff on the site.